Answer: I'm a little confused about your question. If the fruit on your grapevines is drying up, it indicates they are way past harvest stage and are becoming raisins. Next year you need to harvest earlier! You can taste test the grapes for ripeness by picking just one from a cluster. If it's sweet and ripe, it's time to begin harvesting; if it's still rather tangy, wait a week and test again.
If the leaves on your grapevines are dying down, it's a natural process and signals the end of the growing season for them. Don't fertilize this late in the year - fertilizer encourages new growth which will not have time to harden off before winter weather arrives.
Grapevines generally do not need to be fertilized. In fact, too much nitrogen fertilizer will result in lush, green growth at the expense of fruit. All you'll need to provide your grapevines is enough water to keep them healthy during the summer growing season.
Enjoy the fruits of your labor!
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